Language detection follow-up: adding new unit test covering the Detect step in isolation

R=aboxhall,dmazzoni
BUG=889370

Change-Id: I128efc5bf744a18bc7794fcd7d7251d5eb404409
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1520126
Commit-Queue: Chris Hall <chrishall@chromium.org>
Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Auto-Submit: Chris Hall <chrishall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642397}
1 file changed